I have this list which has order and order_details. I want to update the quantity field inside order details by subtracting it with the quantity_kot field.

[
  %Od.Orders.Order{
    __meta__: #Ecto.Schema.Metadata<:loaded, "orders">,
    created_at: ~N[2022-02-08 07:05:35],
    email: test@gmail.com,
    name: Test,
    order_details: [
      %Od.Orders.OrderDetails{
        __meta__: #Ecto.Schema.Metadata<:loaded, "order_details">,
        created_at: ~N[2022-02-08 07:05:35],
        discount: 0.0,
        id: "7598503c-88ad-11ec-88f0-027d853babb4",
        price: 10.0,
        quantity: 4.0,
        quantity_kot: 0,
      },
      %Od.Orders.OrderDetails{
        __meta__: #Ecto.Schema.Metadata<:loaded, "order_details">,
        created_at: ~N[2022-02-08 07:05:35],
        discount: 0.0,
        id: "7b9e6d2c-88ad-11ec-83e2-027d853babb4",
        price: 10.0,
        quantity: 3.0,
        quantity_kot: 0,
      }
    ],
    overall_discount: 10.5,
    payment_status: "unpaid",
    updated_at: ~N[2022-02-08 07:05:35],
  }
]

I tried to achieve this by using the below code

[updated_lists] =
  for list <- lists do
    for x <- list.order_details do
        x
        |> Map.update!(:quantity, &(&1 - x.quantity_kot))
    end
  end

updated_lists

These updates but the problem is I am getting only the order details from this result. All the fields in order struct is missing.

I want the whole list back with only the quantity field inside the order details to be updated. Any insight on how to achieve this will be greatly appreciated. Thanks.